如何使用Singleton Design Pattern java连接到SQL数据库？

Posted 2021-04-08

此外，谁可以显示与本机代码的区别？例如，使用Java连接到数据库并使用Singleton Design模式执行此操作。使用它有什么好处？

答案

您的连接实例应该被保留，您只能通过getConnection（）方法检索您的连接（Singleton模式的getInstance）

这是一个示例代码;

A - Sample Database Utility Based On Singleton Design Pattern of Gang Of Four

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DBUtil {

    private final String HOST;
    private final String PORT;
    private final String DB_NAME;
    private final String USER;
    private final String PASSWORD;

    private final String TARGET_TABLE;
    private final String COLUMN_NAME;

    private final String CONNECTION_STRING;

    private final String SELECT_ALL_SQL;
    private final String SELECT_COLUMN_SQL;
    private final String INSERT_SQL;

    private Connection conn;

    public DBUtil() {
        // Database Parameters
        HOST                    = "your_host_here";
        PORT                    = "your_port_number_here";
        DB_NAME                 = "your_database_name";
        USER                    = "your_databse_user_here";
        PASSWORD                = "your_database_password_here";

        // Database Tables
        TARGET_TABLE            = "your_table_name";
        COLUMN_NAME             = "your_tables_column_name";

        CONNECTION_STRING       = String.format("jdbc:mysql://%s:%s/%s", HOST, PORT, DB_NAME);

        // Query Strings
        SELECT_ALL_SQL          = String.format("SELECT * FROM %s.%s WHERE id=?", DB_NAME, TARGET_TABLE);
        SELECT_COLUMN_SQL       = String.format("SELECT %s FROM %s.%s WHERE id=?", COLUMN_NAME, DB_NAME, TARGET_TABLE);
        INSERT_SQL              = String.format("INSERT INTO %s.%s (id, name) values (?, ?)", DB_NAME, TARGET_TABLE);

        printConfiguration();

        conn = null;
    }

    private void printConfiguration() {
        System.out.println("******************************************************************************");
        System.out.println("DB_NAME                    : " + DB_NAME);
        System.out.println("USERNAME                   : " + USER);
        System.out.println("PASSWORD                   : " + PASSWORD);
        System.out.println("CAMT TABLE                 : " + TARGET_TABLE);
        System.out.println("******************************************************************************");
    }

    private void getConnection() {
        if(conn != null) {
            System.out.println("Connection already established with db");

            return;
        }

        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection(CONNECTION_STRING, USER, PASSWORD);
        } catch (ClassNotFoundException e) {
            System.out.println("Connection FAILED");
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public void closeConnection() {
        if(conn == null) {
            return;
        }

        try {
            conn.close();

            conn = null;
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public int insert(int id, String column) {
        int rowNum;

        getConnection();
        PreparedStatement preparedStatement = null;

        try {
            preparedStatement = conn.prepareStatement(INSERT_SQL);
            System.out.println("SQL: " + INSERT_SQL);
            preparedStatement.setInt(1, id);
            preparedStatement.setString(2, column);

            rowNum = preparedStatement.executeUpdate();

            System.out.println(rowNum + " rows are inserted");

            return rowNum;
        } catch (SQLException e) {
            e.printStackTrace();
        }

        return -1;
    }

    public Model getModel(int id) {
        getConnection();
        PreparedStatement preparedStatement = null;
        Model model = new Model();

        try {
            preparedStatement = conn.prepareStatement(SELECT_ALL_SQL);
            System.out.println("SQL: " + SELECT_ALL_SQL);
            preparedStatement.setInt(1, id);

            ResultSet rs = preparedStatement.executeQuery();

            if(rs.next()) {
                model.setId(rs.getInt("id"));
                model.setName(rs.getString("name"));
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }

        return model;
    }

    public String getName(int id) {
        getConnection();
        PreparedStatement preparedStatement = null;
        String name = null;

        try {
            preparedStatement = conn.prepareStatement(SELECT_COLUMN_SQL);
            System.out.println("SQL: " + SELECT_ALL_SQL);
            preparedStatement.setInt(1, id);

            ResultSet rs = preparedStatement.executeQuery();

            if(rs.next()) {
                name = rs.getString("name");
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }

        return name;
    }

}

B - Model Used in Singleton Database Utility Demo

public class Model {

    private int id;
    private String name;

    public Model() {}

    public Model(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}